Method of Controlling Breakdown Voltage of a Diode Having a Semiconductor Body

ABSTRACT

A diode includes a semiconductor body, a first emitter region of a first conductivity type, a second emitter region of a second conductivity type, a base region arranged between the first and second emitter regions and having a lower doping concentration than the first and second emitter regions, a first emitter electrode electrically coupled to the first emitter region, a second emitter electrode in electrical contact with the second emitter region, a control electrode arrangement comprising a first control electrode section and a first dielectric layer arranged between the first control electrode section and the semiconductor body, and at least one pn junction extending to the first dielectric layer, or arranged distant to the first dielectric layer by less than 250 nm. The breakdown voltage of the diode is adjusted by applying a control potential to the first control electrode section.

TECHNICAL FIELD

Embodiments of the present invention relate to a diode, in particular adiode with a controllable breakdown voltage.

BACKGROUND

Diodes are rectifying elements which conduct a current when they areforward biased and which block when they are reverse biased. When,however, the reverse voltage is higher than a breakdown voltage of thediode, a current can also flow in the reverse direction. Some types ofdiodes, like Zener diodes or avalanche diodes have a well definedbreakdown voltage, which makes these diodes suitable to be used asvoltage limiting elements or as reference voltage generating elements.

The breakdown voltage in conventional diodes is mainly given by thedoping concentrations of the individual semiconductor regions that formthe diode and by the diode layout. Thus, the breakdown voltage inconventional diodes is fixed. However, especially in applications inwhich a diode is used as a voltage limiting element or as a referencevoltage generating element, it may be desirable to vary the breakdownvoltage within a given range.

SUMMARY

A first embodiment relates to a diode, including: a semiconductor body;a first emitter region of a first conductivity type; a second emitterregion of a second conductivity type; a base region arranged between thefirst and second emitter regions and having a lower doping concentrationthan the first and second emitter region; a first emitter electrode onlyelectrically coupled to the first emitter region; a second emitterelectrode in electrical contact with the second emitter region; acontrol electrode arrangement including a first control electrodesection, and a first dielectric layer, the first dielectric layer beingarranged between the first control electrode section and thesemiconductor body; and at least one pn junction extending to the firstdielectric layer or arranged distant to the first dielectric layer byless than 250 nm.

A second embodiment relates to a method of controlling the breakdownvoltage of a diode including a control electrode arrangement including afirst control electrode section, and a first dielectric layer arrangedbetween the first control electrode section and a semiconductor body,and at least one pn junction extending to the first dielectric layer orarranged distant to the first dielectric layer by less than 250 nm. Themethod comprises adjusting the breakdown voltage by applying a controlpotential to the first control electrode section.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be explained with reference to thedrawings. The drawings serve to illustrate the basic principle, so thatonly features necessary for understanding the basic principle areillustrated. The drawings are not to scale. Like reference numbersdenote like features throughout the drawings. In the drawings:

FIG. 1 schematically illustrates a vertical cross section through asemiconductor body in which a diode with a control arrangement and anadjustable breakdown voltage is integrated;

FIG. 2 illustrates a first embodiment of the control arrangement of thediode of FIG. 1;

FIG. 3 illustrates a second embodiment of a control arrangement of thediode of FIG. 1;

FIG. 4 schematically illustrates the breakdown voltage of a diode with acontrol arrangement dependent on a control voltage applied to thecontrol arrangement;

FIG. 5 illustrates a further embodiment of a vertical diode with acontrol arrangement;

FIG. 6 illustrates an embodiment of a vertical diode that is amodification of the diode of FIG. 1;

FIG. 7 illustrates a further embodiment of a vertical diode withadjustable breakdown voltage;

FIGS. 8A to 8C illustrate respective horizontal and vertical crosssections through a semiconductor body in which a lateral diode accordingto one embodiment is integrated;

FIG. 9 illustrates a lateral Zener diode according to a firstembodiment;

FIG. 10 illustrates a lateral Zener diode according to a secondembodiment;

FIG. 11 illustrates a lateral Zener diode according to a thirdembodiment;

FIG. 12 illustrates a lateral Zener diode according to a fourthembodiment;

FIG. 13 illustrates characteristic curves of the Zener diodes accordingto FIGS. 9 to 12.

DETAILED DESCRIPTION

FIG. 1 illustrates a first embodiment of a diode with adjustablebreakdown voltage. The diode illustrated in FIG. 1 is a vertical diodewhich includes a first emitter region 11 of a first conductivity type,and a second emitter region 12 of a second conductivity type which iscomplementary to the first conductivity type. The first and secondemitter regions 11, 12 are implemented in a semiconductor body 100 whichincludes a first surface 101 and a second surface 102 opposite to thefirst surface 101. In this embodiment, the first emitter region 11 isarranged near the first surface 101, and the second emitter region 12 isarranged near the second surface 102. The first and second emitterregions 11, 12 are arranged distant from one another in a verticaldirection of the semiconductor body 100, wherein the vertical directionof the semiconductor body 100 is a direction which extends perpendicularto the first and second surfaces 101, 102. The semiconductor body 100is, for example, made of silicon or any other suitable semiconductormaterial.

The diode further includes a base region 13 arranged between the firstemitter region 11 and the second emitter region 12. The base region 13is more lowly doped than the first and second emitter regions 11, 12 andis either of the first conductivity type or of the second conductivitytype. For explanation purposes it is assumed that the first emitterregion 11 is p-doped so as to form a p-emitter of the diode, that thesecond emitter region 12 is n-doped so as to form an n-emitter of thediode, and that the base region 13 is n-doped. The doping concentrationof the p-emitter 11 is, for example, in the range of between 1e16 cm⁻³(1·10¹⁶ cm⁻³) and 1e20 cm⁻³ (1·10²⁰ cm⁻³). The doping concentration ofthe p-emitter may be rather constant throughout the p-emitter or mayvary. According to one embodiment, the doping concentration of thep-emitter varies according to a Gaussian curve in a vertical direction,which is a direction perpendicular to the first surface 101. The dopingconcentration of the n-emitter is, for example, in the range of between1e16 cm⁻³ and 1e20 cm⁻³, and the doping concentration of the base region13 is, for example, in the range of between 5e13 cm⁻³ and 1e13 cm⁻. In adiode with an n-type base region 13 a pn-junction is formed between thep-emitter 11 and the base region 13.

Referring to FIG. 1, the diode further includes a first electrode 31which electrically contacts the first emitter region 11, and a secondelectrode 32 which electrically contacts the second emitter region 12.In the embodiment illustrated in FIG. 1, the first electrode 31 isarranged on the first surface 101 and the second electrode 32 isarranged on the second surface 102 of the semiconductor body. When thefirst emitter region 11 is a p-emitter, the first electrode 31 forms ananode terminal A of the diode, while the second electrode 32 forms acathode terminal K of the diode. This diode is conducting when apositive voltage higher than a forward voltage of the diode is appliedbetween the anode A and the cathode K terminals. In a diode implementedin a silicon semiconductor body the forward voltage is about 0.7V. Thediode is blocking when a positive voltage is applied between the cathodeK and the anode A terminal (or when a negative voltage is appliedbetween the anode A and the cathode K terminals). A positive voltagebetween the cathode K and the anode A terminals will be referred to asreverse voltage in the following. When, however, the reverse voltagereaches a breakdown voltage threshold—which is significantly higher thanthe forward voltage of the diode—the diode conducts a current in itsreverse direction. This is a commonly known mechanism. In the diode ofFIG. 1, however, the breakdown voltage threshold can be adjusted duringoperation of the diode. For this purpose the diode includes a controlarrangement with a first control electrode section 21 ₁ and a secondcontrol electrode section 21 ₂ which are dielectrically insulated fromthe semiconductor body 100 by a first dielectric layer 22 ₁ and a seconddielectric layer 22 ₂, respectively. In the diode illustrated in FIG. 1,the first and second control electrode sections 21 ₁, 21 ₂ are arrangedin trenches which extend into the semiconductor body 100. In theembodiment illustrated in FIG. 1, these trenches extend into thesemiconductor body 100 from the first surface 101.

The control electrode sections 21 ₁, 21 ₂ are arranged distant from oneanother in a horizontal direction (which extends perpendicular to thevertical direction) of the semiconductor body 100. The first emitterregion 11 is arranged between the two control electrode sections 21 ₁,21 ₂ in this horizontal direction, and a pn-junction between the firstemitter region 11 and the base region 13 in this horizontal directionextends to the first and second dielectric layers 22, which insulate thefirst and second control electrode sections 21 ₁, 21 ₂ from thesemiconductor body 100.

In the diode of FIG. 1, the base region 13 extends in a verticaldirection of the semiconductor body 100 from the first emitter region 11to the second emitter region 12. A length l of the base region 13 isdefined by a (shortest) distance between the first emitter region 11 andthe second emitter region 12. The base region 13 is at least partiallyarranged between the first and second control electrode sections 21 ₁,21 ₂ and the first and second dielectric layers 22 ₁, 22 ₂,respectively. Adjacent to the base region 13 the first and secondcontrol electrode sections 21 ₁, 21 ₂ extend along at least 25%, 50%,75% or even 100% of the length l of the base region 13. In other words:A distance in the vertical direction of the semiconductor body 100between the second emitter region 12 and the first and second controlelectrode sections 21 ₁, 21 ₂ is less than 75%, 50%, 25% or even 0% ofthe length l of the base region 13. In the last mentioned case, thecontrol electrode sections 21 ₁, 21 ₁ surrounded by the first and seconddielectric layers 22 ₁, 22 ₂ extend to or into the second emitter region12.

The control electrode sections 21 ₁, 21 ₂ include an electricallyconducting material, such as a metal or a highly doped polycrystallinesemiconductor material. Suitable metals are, for example, copper (Cu),titanium (Ti), aluminum (Al), or tungsten (W). A suitablepolycrystalline semiconductor material is, for example, polysilicon. Thedielectric layers 22 ₁, 22 ₂ may include a conventional dielectricmaterial, like an oxide or a nitride. According to one embodiment, thedielectric layers are implemented as composite layers which include atleast two different dielectric layers.

The first and second control electrode sections 21 ₁, 21 ₂ serve toadjust a breakdown voltage of the diode. For this purpose, each of thesecontrol electrode sections 21 ₁, 21 ₂ includes a control terminal C1 andC2, respectively. According to one embodiment, these two controlterminals C1, C2 have different control voltages or control potentialsconnected thereto. According to another embodiment these controlterminals C1, C2 are connected to a terminal for a common controlpotential.

A semiconductor region between the trenches with the control electrodesections 21 ₁, 21 ₂ will be referred to as mesa region in the following.A width of this mesa region, which is a distance between the controlelectrode sections 21 ₁, 21 ₂ is d, wherein d is, e.g., between about0.3 μm and 10 μm.

FIGS. 2 and 3 show horizontal cross sections through the diode of FIG. 1in a horizontal section plane X-X to illustrate two differentimplementation examples of the control electrode sections 21 ₁, 21 ₂. Inthe embodiment illustrated in FIG. 2, the first and second controlelectrode sections 21 ₁, 21 ₂ are longitudinal electrodes which extendparallel to each other in a horizontal direction of the semiconductorbody. In the embodiment illustrated in FIG. 3, the first and secondcontrol electrode sections 21 ₁, 21 ₂ are part of one control electrode21 which—as seen in the horizontal plane X-X—has a rectangular geometry.The first and second control electrode sections 21 ₁, 21 ₂ are formed bythose sections of the rectangular electrode 21 which are arrangedopposite to each other. Optionally, these sections are dielectricallyinsulated from one another by dielectric layers 22 ₃, 22 ₄ (illustratedin dashed lines). Providing these dielectric layers 22 ₃, 22 ₄ makes itpossible to apply different control potentials to the individual controlelectrode sections 21 ₁, 21 ₂. Having a control electrode with arectangular geometry is only an example. Any other closed-loop geometry,like a circular geometry, may be used as well.

FIG. 4 schematically illustrates the operating principle of the diodeillustrated in FIG. 1. FIG. 4 shows the breakdown voltage threshold orbreakdown voltage V_(BD) dependent on a control potential or controlvoltage V_(C) applied to the control terminals C1, C2. FIG. 4 shows twocurves which illustrate the breakdown voltage V_(BD) versus the controlvoltage V_(C) for two different diodes which have different thicknesses(dielectric thicknesses) of the dielectric layers 22 ₁ and 22 ₂ (seeFIG. 1).

The curves illustrated in FIG. 4 were obtained by simulating a devicewith a trench depth of about 2.2 μm, a mesa width of about 0.9 μm and adoping concentration of the base region 13 between about 5e16 cm⁻³ and1e17 cm⁻³ . The first curve labeled with d1 represents a dielectricthickness of 80 nm while the curve labeled with d2 represents a largerthickness of 120 nm.

The control voltage V_(C) is a voltage between the control terminals C1,C2 and the anode terminal A of the diode. In the diode for which thesimulation results illustrated in FIG. 4 were obtained, the same controlvoltage V_(C) was applied to both control terminals C1, C2. In FIG. 4 acontrol voltage range of −15V to +15V is illustrated. However, this isonly an example; dependent on the specific embodiment of the diode othercontrol voltage ranges may be applied as well. Generally, the breakdownvoltage V_(BD) increase with increasing control voltage V_(C) until amaximum breakdown voltage V_(BDmax) is reached, and starting from thismaximum breakdown voltage V_(BDmax) the breakdown voltage V_(BD)decreases with further increasing control voltage V_(C).

Referring to FIG. 4, the characteristic curves which illustrate thebreakdown voltage V_(BD) dependent on the control voltage V_(C) have twosections: a first section in which the breakdown voltage V_(BD)increases with increasing control voltage V_(C); and a second section inwhich the breakdown voltage V_(BD) decreases with increasing controlvoltage V_(C). A certain breakdown voltage V_(BD), like breakdownvoltage V_(BD0) illustrated in FIG. 4, can be obtained with twodifferent control voltages, a first voltage V_(C1) in the first sectionand a second voltage V_(C2) in the second section. In other words: Thebreakdown voltage is V_(BD0) when the control voltage V_(C) is eitherV_(C1) or V_(C2). The maximum breakdown voltage V_(BDmax) is obtainedwhen the control voltage V_(C) is V_(Cmax) in the embodiment illustratedin FIG. 4. Control voltages V_(C) smaller than V_(Cmax) define the firstsection of the characteristic curves, and control voltages V_(C) higherthan V_(Cmax) define the second section of the characteristic curves.

When the reverse voltage applied to the diode reaches the breakdownvoltage V_(BD), which is adjusted by suitably selecting the controlvoltage V_(C), a breakdown, specifically an avalanche breakdown, occurs.In the component illustrated in FIG. 1, two different types of breakdownmay occur: a first type in which the breakdown first occurs in theregion of the bottoms of the trenches in which the first and secondcontrol electrode sections 21 ₁, 21 ₂ are arranged; and a second type ofbreakdown in which the breakdown first occurs in the region between thetrenches with the first and second control electrode sections 21 ₁, 21₂. The first type of breakdown occurs when the control voltage V_(C) isselected such that it is smaller than V_(Cmax), i.e. when thecorresponding breakdown voltage is in the first section of thecharacteristic curve, and the second type of breakdown occurs when thecontrol voltage V_(C) is higher than V_(Cmax), i.e. when thecorresponding breakdown voltage is in the second (falling) section ofthe characteristic curve. According to one embodiment, the controlvoltage for adjusting the breakdown voltage is selected from the secondcontrol voltage range. Using this voltage range a degradation of thebreakdown characteristics can be avoided because avalanchemultiplication occurs distant from semiconductor dielectric interfacesbetween the dielectric layers 22 ₁, 22 ₂ and the base region 13.

In the embodiment illustrated in FIG. 4, the breakdown voltage can bevaried between about 40V and about 15V by suitably selecting the controlvoltage V_(C) from the second control voltage range. It goes withoutsaying that these are only exemplary voltages. Dependent on the dopingconcentrations of the individual semiconductor regions of the diode anddependent on design parameters, like the length of the base region 13,the dielectric thickness or the distance between the control electrodesections 21 ₁, 21 ₂—which defines a width of the base region 13—otherbreakdown voltage values can be obtained as well.

Referring to FIG. 1, the diode optionally includes a higher doped region14 of the first conductivity type within the first emitter region 11.This higher doped region 14 is connected to the first electrode 31, andits geometry is such that it extends further to the pn-junction betweenthe first emitter 11 and the base region 13 in the middle of the mesaregion. The higher doped region 14 serves to provide a low-ohmic contactbetween the first electrode 31 and the first emitter region 11. Further,the higher doped region 14 can define the position at which theavalanche breakdown occurs first when the breakdown voltage is reached.In the embodiment illustrated in FIG. 1, this position is in the middleof the mesa region between the two trenches.

The control voltage V_(C) is a voltage between the control terminals C1,C2 and the anode terminal A of the component. According to oneembodiment, the same control voltage V_(C) is applied between each ofthe control terminals C1, C2 and the anode terminal A. According to afurther embodiment, one of the control terminals is electricallyconnected with the anode terminal, while the control voltage V_(C) isonly applied between the other one of the control terminals and theanode terminal A. A positive control voltage V_(C) is a positive voltagebetween the control terminal and the anode terminal A, and a negativecontrol voltage V_(C) is a negative voltage between the control terminaland the anode terminal A.

The basic structure of the diode illustrated in FIG. 1 is similar to theparasitic body diode in a trench MOSFET. However, the diode, unlike aMOSFET, does not include a source region, so that in the diode there arenot two semiconductor regions of the same doping type—like the sourceregion and the drift region in a MOSFET—between which a conductingchannel may occur induced by a gate electrode. Thus, the first electrode31 of the diode is only connected to the first emitter region 11 and tothe optional higher doped region 14 of the same doping type as the firstemitter region 11, but is not also connected to a complementarily dopedsemiconductor region (like the source region in a MOSFET). In the diodeaccording to FIG. 1, the control voltage applied between the controlterminals C1, C2 and the anode terminal A only serves to adjust thebreakdown voltage of the diode whereas in the presence of a sourceregion a conductive channel would be opened when applying a controlvoltage to the control electrodes 21 ₁, 21 ₂.

A diode as illustrated in FIG. 1 can be used as a voltage limitingelement which serves to limit the voltage across another electronicdevice (not shown in FIG. 1). The diode can be connected in parallelwith the other electronic device and limits the voltage drop across theparallel circuit, and therefore across the other electronic device, to avoltage defined by the breakdown voltage of the diode. The diode couldalso be used to generate a reference voltage. For this, a reversecurrent is applied to the diode. The voltage drop (in the reversedirection) of the diode then equals the breakdown voltage of the diodeand may be used as a reference voltage. This reference voltage can beadjusted by applying a suitably selected control voltage V_(C) betweenthe control terminals C1, C2 and the anode terminal A.

The basic principle of the diode illustrated in FIG. 1 has beenexplained based on a diode with a p-doped first emitter region 11 and ann-doped second emitter region 12. In this case, the first electrode 31forms an anode terminal A, and the second electrode 32 forms a cathodeterminal K. The basic principle of adjusting the breakdown voltage is,however, not restricted to be used in this specific type of diode. In afurther embodiment, the first emitter region 11 is n-doped so that thefirst electrode 31 forms a cathode terminal, while the second emitterregion 12 is p-doped, so that the second electrode 32 forms an anodeterminal.

FIG. 5 illustrates a further embodiment of a diode with adjustablebreakdown voltage. The embodiment illustrated in FIG. 5 is differentfrom the embodiment illustrated in FIG. 1 in that the dielectric layers22 ₁, 22 ₂ have thicknesses which increase in the direction of thebottom of the trenches. In the embodiment illustrated in FIG. 5, thesedielectric layers 22 ₁, 22 ₂ basically have two different thicknesses: afirst thickness in a region adjacent to the first emitter region 11 anda second (higher) thickness adjacent to the base region 13. This,however, is only an example. It is also possible to have more than twodifferent thicknesses of the dielectric layers 22 ₁, 22 ₂. It is alsopossible to have the thicknesses of the two dielectric layers 22 ₁, 22 ₂increase gradually so as to have a lowest thickness at the top of thetrenches, i.e. in the region of the first surface 101, and the highestthickness at the bottom of the trenches.

Referring to FIG. 5, it is also possible for the control electrodes tohave two or more different electrode sections arranged one above theother in the trench. This is illustrated for the second controlelectrode section 21 ₂ in FIG. 1. In this connection it should bementioned that only one of the control electrode sections or both of thecontrol electrode sections can be implemented with several separatedelectrode sections arranged in one trench. In the embodiment illustratedin FIG. 5, the second control electrode section 21 ₂ includes twoelectrodes: a first electrode 21 ₂₁ in the upper region of the trench;and a second electrode 21 ₂₂ in the lower section of the trench.According to one embodiment, the control voltage is applied to both ofthese electrodes 21 ₂₁, 21 ₂₂. According to a further embodiment, thecontrol voltage (like the control voltage V_(C) illustrated in FIG. 4)is applied only to the second electrode 21 ₂₂ in the lower trenchsection and arranged adjacent to the base region 13, while the firstelectrode 21 ₂₁ in the upper trench region and adjacent to the firstemitter 11 is connected to the first electrode 31 or the anode terminalA, respectively.

Further, it is also possible to provide at least two separate electrodesof the control electrode sections without varying the thickness of thedielectric layers 22 ₁, 22 ₂.

The diodes illustrated in FIGS. 1 and 5 are vertical diodes, because inthese diodes a forward current or a breakdown current—dependent onwhether the diode is forward biased or reverse biased—essentially flowsin a vertical direction of the semiconductor body 100 between the firstand second emitter regions 11, 12. In the diodes illustrated in FIGS. 1and 5 the first and second electrodes 31, 32 are arranged on theopposite first and second surfaces 101, 102 of the semiconductor body100.

FIG. 6 illustrates a further embodiment of a vertical diode. In thisdiode the second emitter 12 is implemented as a buried layer which inthe vertical direction of the semiconductor body 100 is arranged distantto the first emitter region 11. This buried second emitter 12 is alsoarranged distant to the second surface 102 of the semiconductor body.Between the second emitter 12 and the second surface 102 a semiconductorregion can be arranged which is doped complementarily to the secondemitter 12. In the diode of FIG. 6, the second electrode 32 is arrangedon the first surface 101 distant to the first electrode 31. The secondemitter 12 is electrically connected to the second electrode 32 via aconnection region 12′—which is also referred to as sinker—of the sameconductivity type as the second emitter 12. In this embodiment, theconnection region 12′ is arranged outside the mesa region.

According to a further embodiment (not shown), the connection region 12′is arranged in the mesa region at a position that is distant to thefirst emitter region in a direction that is perpendicular to the sectionplane shown in FIG. 6.

FIG. 7 illustrates a further embodiment of a vertical diode withadjustable breakdown voltage. The diode according to FIG. 7 is amodification of the diode of FIG. 1 and is obtained from the diode ofFIG. 1 by omitting one of the control electrode sections, such as thesecond control electrode section 21 ₂. The operating principle of thediode of FIG. 7 corresponds to the operating principle of the diode ofFIG. 1 with the difference that the breakdown voltage is adjusted usingonly one control electrode section. The embodiments illustrated in FIGS.5 and 6 as well as the embodiments explained below can be modified inthe same way by omitting one of the control electrode sections, such asthe second control electrode section 21 ₂.

According to one embodiment illustrated in dashed lines in FIG. 7, thefirst emitter region 11 does not extend to the first dielectric layer 22₁ in a horizontal direction but is arranged distant to the firstdielectric layer 22 ₁, 22 ₂. The distance is, for example, between 50 nmand 250 nm, or less. In this case, the pn junction between the emitterregion 11 and the base region is also distant to the first dielectriclayer 22 ₁, the distance being less than 200 nm.

FIGS. 8A to 8C illustrate an embodiment of a lateral diode withadjustable breakdown voltage. FIG. 8A illustrates a top view on thefirst surface 101 of a semiconductor body 100 in which the diode isintegrated, FIG. 8B illustrates a vertical cross section in a verticalsection plane Y-Y, and FIG. 8C illustrates a vertical cross section in avertical section plane Z-Z. In this diode, the first and second emitterregions 11, 12 are arranged distant from one another in a lateral orfirst horizontal direction of the semiconductor body 100. The first andsecond control electrode sections 21 ₁, 21 ₂ are arranged distant fromone another in a second horizontal direction which is perpendicular tothe first horizontal direction, and these control electrode sections 21₁, 21 ₂ extend in the first horizontal direction between the firstemitter region 11 and the second emitter region 12. A length l of thebase region 13 is defined by the dimension of the base region 13 in thefirst horizontal direction between the first and the second emitterregions. The first and second control electrode sections 21 ₁, 21 ₂extend along the base region 13 in this first horizontal direction.Everything which has been explained concerning the relationship betweenthe lengths l of the base region 13 and the extension of the first andsecond control electrode sections 21 ₁, 21 ₂ in the current flowdirection of the component, and concerning the dopant concentrations andthe design parameters applies to the lateral component of FIGS. 8A to 8Caccordingly. A vertical cross section through the base region 13 isillustrated in FIG. 8B.

FIG. 8C illustrates a cross section through one of the control electrodesections, namely the second control electrode section 21 ₂. The firstcontrol electrode section 21 ₁ can be implemented equivalently. Thecontrol electrode sections 21 ₁, 21 ₂, referring to FIG. 8C, also extendin the vertical direction 100 of the semiconductor body, wherein thebase region 13 and at least the first emitter region 11 also extend inthe vertical direction of the semiconductor body 100. In the embodimentillustrated in FIGS. 8A to 8C the dielectric layers 22 ₁, 22 ₂ havedifferent thicknesses. However, this is only an example. Thesedielectric layers could also be implemented to have a constantthickness. Further, a control electrode section could be implementedwith several separate electrodes, which has been explained withreference to FIG. 5 herein before.

In the lateral diode of FIGS. 8A to 8C the first and second electrodes31, 32 contacting the first and second emitter regions 11, 12,respectively, are arranged on the first side 101 of the semiconductorbody 100. A second surface 102 of the semiconductor body is, forexample, formed by a semiconductor substrate 110. The substrate can bedoped complementarily to the base region 13 or can have the same dopingtype as the base region 13. Referring to FIG. 8C, the control electrodesections do not extend into the substrate 110. However, this is only anexample. The trenches with the control electrode sections 21 ₁, 21 ₂could also extend into the substrate.

While in the embodiment illustrated in FIG. 8B the first emitter regionadjoins the substrate, the first emitter region could also be arrangeddistant to the substrate 110 as illustrated in dashed lines in FIG. 8B.In this case, a section of the base region 13 is arranged between thefirst emitter region 11 and the substrate 110.

Optionally the diode includes a higher doped semiconductor region 14 ofthe first conductivity type in the first emitter region 11. Thissemiconductor region 14 in the middle of the mesa region between thecontrol electrode sections 21 ₁, 21 ₂ extends laterally further to thesecond emitter region 13 than in other regions, so that the position atwhich an avalanche breakdown occurs first is in the middle of the mesaregion.

FIG. 9 illustrates a further embodiment of a diode with adjustablebreakdown voltage. In this diode the first and second emitter regions11, 12 are arranged distant from one another in a horizontal directionof the semiconductor body 100 and are arranged in the region of thefirst surface 101 of the semiconductor body. The first and secondemitter regions 11, 12 are electrically contacted by the first andsecond electrodes 31, 32, respectively, which are arranged on the firstsurface 101. For explanation purposes it is assumed that the firstemitter region 11 is p-doped and that the second emitter region 12 isn-doped, so that the first electrode 31 forms an anode terminal A andthe second electrode 32 forms a cathode terminal K of the diode.

The first and second emitter regions 11, 12 are both arranged betweenthe trenches with the first and second control electrode sections 21 ₁,21 ₂. These trenches extend in a vertical direction of the semiconductorbody 100 from the first surface 101. The first and second gate electrodesections 21 ₁, 21 ₂ are dielectrically insulated from the semiconductorbody 100 by the first and second dielectric layers 22 ₁, 22 ₂. Thesedielectric layers 22 ₁, 22 ₂ can be implemented like the dielectriclayers 22 ₁, 22 ₂ of FIGS. 1, 5 and 6.

The second trench as well as the second control electrode 21 ₂ and thesecond dielectric layer 22 ₂ mainly serve as a lateral insulation trenchstructure and can be omitted in other embodiments. Thus, this electrode21 ₂ and the surrounding dielectric layer 22 ₂ are illustrated in dashedlines in FIG. 9.

The base region 13 is arranged between the first and second emitterregions 11, 12. In the embodiment illustrated in FIG. 9, the base region13 in the horizontal direction extends from the trench with the firstcontrol electrode section 21 ₁, and the first dielectric layer 22 ₁ tothe second trench with the second control electrode section 21 ₂ and thesecond dielectric layer 22 ₂. In the vertical direction the base region13 extends further into the semiconductor body 100 than the first andsecond emitter regions 11, 12. In the embodiment illustrated in FIG. 9,the base region 13 is completely arranged between the trenches, i.e. thebase region 13 in the vertical direction of the semiconductor body 100does not extend below the trenches with the first and second gateelectrode sections 21 ₁, 21 ₂.

In another embodiment (not illustrated) the base region 13 extends belowthe trenches with the first and second control electrode sections 21 ₁,21 ₂ in the vertical direction of the semiconductor body 100.

The diode illustrated in FIG. 9 is implemented as a Zener diode. In thisdiode, the base region 13 is of the first conductivity type, i.e. of thesame conductivity type as the first emitter region 11, while inembodiments of the diode according to FIGS. 1, 5, 6 and 7 the baseregion is doped complementary to the first emitter region. In the baseregion 13 a Zener region 15 is arranged that is higher doped thanremaining sections of the base region 13. According to one embodiment,the Zener region is of the first conductivity type, which is theconductivity type of the first emitter region 11 and the base region 13.According to a further embodiment, the Zener region 15 is of the secondconductivity type, which is the conductivity type of the second emitterregion 12. Dependent on the conductivity type of the Zener region 15,the pn-junction is either formed between the Zener region 15 and thesecond emitter region 12 or between the Zener region 15 and the baseregion 13.

In the embodiment illustrated in FIG. 9, the Zener region 15 adjoins thesecond emitter region in the vertical direction of the semiconductorbody 100. The Zener region 15 does not completely surround the secondemitter region 12, so that there are regions in which the second emitterregion 12 adjoins the base region 13. When the Zener region 15 has thesecond conductivity type and when the breakdown voltage of the diode isreached, an avalanche breakdown occurs at a position where the baseregion 13 adjoins the second emitter region 12.

The doping concentrations of the individual semiconductor regions are,for example, as follows: first emitter region 11: between 1e18 cm⁻³ and1e21 cm⁻³; second emitter region 12: between 1e18 cm⁻³ and 1e21 cm⁻³ ;base region 13: between 1e14 cm⁻³ and 1e18 cm⁻³; Zener region 15:between 1e16 cm⁻³ and 1e19 cm⁻³ .

Vertical dimensions of the semiconductor regions, which are dimensionsin a direction perpendicular to first surface 101 are, for example, asfollows: first emitter region 11: between 0.1 μm and 1 μm; secondemitter region 12: between 0.1 μm and 1 μm; Zener region 15: between 0.2μm and 2 μm.

Lateral dimensions of the individual semiconductor regions in thesection plane illustrated in FIG. 9 are, for example, as follows: firstemitter region 11: between 20 nm and several μm; second emitter region12: between 20 nm and several μm; base region 13: between 500 nm andseveral μm, where this dimension may correspond to a mesa width betweenthe control electrode sections 21 ₁, 21 ₂. The lateral dimension of theZener region 15 is such that it is smaller than the lateral dimension ofthe second emitter region 12 it adjoins. Further, a vertical dimension(depth) of the base region 13 should be chosen such that a Zener(breakthrough) voltage between the second emitter region 12 and theZener region 15 is smaller than an Avalanche breakthrough voltagebetween a semiconductor layer 40 on which the base region 13 isarranged, the base region 13, the Zener region 15 and the first emitterregion 12.

In the diode of FIG. 9, the base region 13—in which the emitter regions11, 12 are arranged—is arranged above a semiconductor layer 40.According to one embodiment, the semiconductor layer 40 includes twosublayers: a first layer 41 which forms the second surface 102 of thesemiconductor body, and a second semiconductor layer 42 arranged betweenthe first layer 41 and the base region 13 and being more lowly dopedthan the first layer. The first layer 41 is, for example, a substrate.The other semiconductor layers, i.e. the second layer 42 and the layerin which the base region 13 is implemented, can be epitaxial orimplanted and diffused layers. According to one embodiment, a dopingtype of the second layer is complementary to a doping type of the baseregion 13. The first layer (substrate) may have the same doping type asthe second layer or may have a complementary doping type.

While in the embodiment illustrated in FIG. 9, the trench with the firstcontrol electrode section 21 ₁ and the trench with the optional secondcontrol electrode section 21 ₂ extend through the base region 13, sothat these trenches extend deeper into the semiconductor body 100 thanthe base region 13, it is also possible to implement the base region 13such that it extends beyond the trench(es) as seen from the firstsurface 101.

According to one embodiment, the semiconductor layer 40 includes aterminal T to apply an electrical potential at this semiconductor layer40. This electrical potential is, for example, selected such that theinjection of minority charge carriers from the base region 13 into thesemiconductor layer 40 is prevented when the diode is in operation.According to one embodiment, the electrical potential applied to thisterminal T is, for example, in the range of between 0V and 1000V, inparticular between 0V and 400V. By suitably selecting the dopingconcentration of the base region 13 and the semiconductor layer 42, avoltage blocking capability between the diode, which means betweendevice regions of the diode, and the semiconductor layer 40 can beadjusted. Dependent on the doping concentration and thickness of thebase region 13 and the second semiconductor layer 42, this voltageblocking capability may range between 0V and 1000V.

FIG. 10 illustrates a further embodiment of a Zener diode. The Zenerdiode illustrated in FIG. 10 is based on the Zener diode illustrated inFIG. 9, so that in the following only those feature of the Zener diodeof FIG. 10 that are different from the Zener diode of FIG. 9 will beexplained.

In the Zener diode of FIG. 10, the first conductivity type is an n-type,while the second conductivity type is a p-type. Thus, the first emitterregion 11 is an n-emitter and the second emitter region is a p-emitter,so that the first electrode 31 forms a cathode terminal and the secondelectrode 32 forms an anode terminal of the Zener diode. The base region13 and the Zener region 15 are both of the first conductivity type, sothat a pn-junction is formed between the Zener region 15 and the secondemitter region 12. An n-doping of the base region of the diode of FIG.10 instead of a p-doping as in the diode of FIG. 9 helps to reduce theelectrical resistance of the Zener diode when forward biased.

A pn-junction is formed between the base region 13 and the substrate 40.In this embodiment, the substrate 40 includes at least one thirdsemiconductor layer or region 43 adjoining the base region 13 and dopedcomplementarily to the base region. According to one embodiment, thethird region 43 is electrically connected to a further biasing terminalT2. Referring to FIG. 10, the third region 43 may extend to the firstsurface 101 of the semiconductor body and may be electrically connectedto the further terminal T2 at the first surface. A biasing potentialapplied to this further terminal T2 may be a reference potential, suchas ground. The biasing potential is, for example, between 0V and 1000V,in particular between 0V and 700V.

Optionally, the substrate includes a further semiconductor layer 41,corresponding to the first layer 41 of FIG. 9. The doping type of thefirst layer 41 corresponds to the doping type of the base region 13 andis complementary to the doping type of the third layer 43. Optionally, afurther layer 42 corresponding to the second layer 42 of FIG. 9 isarranged between the first layer 41 and the third layer. A doping typeof the second layer corresponds to a doping type of the first layer 41,with the second layer 42 having a lower doping concentration. The firstlayer may be connected to the terminal T for applying a biasingpotential.

FIG. 11 illustrates a modification of the diode illustrated in FIG. 9.In the diode of FIG. 11, the first emitter 11 includes two emittersections: a first emitter section 11 ₁ which in the vertical directionof the semiconductor body 100 is arranged distant to the second emitterregion 12 and which in a horizontal direction may adjoin the firstdielectric layer 22 ₁; and a second emitter section 11 ₂ which isarranged distant to the second emitter 12 in the horizontal directionand which in the vertical direction extends from the first surface 101to the first section 11 ₁ so as to connect the first section 11 ₁ of thefirst emitter to the first electrode 31. The Zener region 15 is arrangedbetween the first section 11 ₁ of the first emitter 11 and the secondemitter 12. In this embodiment, the Zener region 15 adjoins the firstsection 11 ₁ and the second emitter 12. According to one embodiment, theZener region 15 and the second emitter 12 optionally are doped lower inthose regions in which the second emitter 12 and the Zener region 15adjoin one another. These lower doped regions are illustrated in dashedlines and are denoted as 15 ₁ and 12 ₁ in FIG. 11. The substrate layer40, the first emitter section 11 ₁, the base region 13, the Zener region15, the second emitter region 12 and the first control electrode section21 ₁ form a parasitic MOSFET when the substrate layer 40 is dopedcomplementary to the base region 13. A threshold voltage of thisparasitic MOSFET can be adjusted through the doping concentration of thefirst emitter region section 11 ₁, the base region 13 and the Zenerregion 15.

In the embodiment illustrated in FIG. 10, the semiconductor regions ofthe diode are completely arranged between the trenches with the controlelectrode sections 21 ₁, 21 ₂, i.e. also the first section 11 ₁ of thefirst emitter does not extend to below these trenches in thisembodiment.

FIG. 12 illustrates a modification of the diode of FIG. 11. In thisdiode the lower doped region 12 ₁ of the second emitter completelysurrounds the higher doped region within the semiconductor body 100.Thus, unlike in the diode of FIG. 11, the higher doped region of theemitter does not adjoin the base region 13.

According to one embodiment, a ratio between the doping concentration ofthe higher doped region and the lower doped region 12 ₁ of the secondemitter 12 is between 1e2 (100) and 1e5 (10000), and a ratio between thedoping concentration of the higher doped region and the lower dopedregion 15 ₁ of the Zener region 15 is between 2 and 100. The lower dopedregion 12 ₁ of the second emitter region 12, and the lower doped region15 ₁ of the Zener region 15 are, for example, produced in the baseregion by implantation and diffusion processes. The lower doped secondemitter region 12 ₁ can be produced by implanting dopant atoms of thesecond dopant type, such as arsenic (As) atoms in that region of thesecond emitter 12 for which a higher doping concentration is desired andby diffusing the implanted dopant atoms deeper into the base region 13by employing an annealing process. The lower doped Zener region 15 ₁ canbe produced by implanting dopant atoms of the first dopant type, such asBoron (B) atoms in that region of the Zener region 15 for which a higherdoping concentration is desired and by diffusing the implanted dopantatoms into the surrounding regions of the base region. For obtaining adiode as illustrated in FIGS. 11 and 12, the dopant atoms of the firstdopant type, that form the Zener region 15, are implanted deeper intothe semiconductor body 100 than the dopant atoms of the second dopanttype, that form the second emitter region 12. The dopant atoms of thesecond dopant type mainly diffuse deeper into the semiconductor body,which is away from the first surface 101, so as to form the lower dopedregion 12 ₁ below the higher doped region. The dopant atoms of the firstdopant type diffuse into the first section 11 ₁ of the first emitter 11,which is below the Zener region 15, and into the direction of the firstsurface, so as to form the lower doped Zener region 15 ₁ above thehigher doped Zener region.

In the embodiments illustrated in FIGS. 11 and 12, the Zener region 15is arranged between the first emitter region 11, specifically the firstsection 11 ₁ of the first emitter region 11, and the second emitterregion 12. In these embodiments, the Zener region 15 has the function ofa base region, wherein either between the Zener region 15 and the firstemitter region 11 or between the Zener region 15 and the second emitter12 a pn junction is formed and extends to the first dielectric layer 22₁. However, the pn-junction could also be arranged distant to the firstdielectric layer 22 ₁ up to 250 nm.

Like in the diodes illustrated in FIGS. 1, 5 and 6 a breakdown voltageof the diodes illustrated in FIGS. 9, 10, 11 and 12 can be adjusted byapplying a control voltage between the control terminals C1, C2 and oneof the anode and the cathode terminals A, K. According to oneembodiment, the control voltage is applied between the control terminalsC1, C2 and the anode terminal A. According to a further embodiment, thesame control voltage is applied to the first and second controlterminals C1, C2. An avalanche breakdown or Zener breakdown occurs whenthe diode is reverse biased and when the reverse biasing voltage reachesa breakdown voltage which is defined by the control voltage. Theoperating principle of this diode becomes obvious from FIG. 13, in whichseveral characteristic curves are illustrated which show a reversecurrent I_(KA) of the diode dependent on a reverse biasing voltageV_(KA). These characteristic curves were obtained for five differentcontrol voltages V_(C)=V1, V_(C)=V2, V_(C)=V3, V_(C)=V4, and V_(C)=V5.As can be seen from FIG. 13, a significant increase in the reversecurrent I_(KA) occurs when the reverse voltage V_(KA) reaches thresholdvoltages V_(KA1), V_(KA2), V_(KA3), V_(KA4), and V_(KA5). Thesethreshold voltages correspond to the breakdown voltages of the diode.Referring to FIG. 13, these breakdown voltages are dependent on thecontrol voltage. According to one embodiment, V1=−15V, V2=−10V, V3=−5V,V4=0V, and V5=+5V.

Although the operating principle of the diode illustrated in FIGS. 9 to11 has been explained with reference to a diode in which the firstemitter 11 is p-doped and the second emitter 12 is n-doped, it should benoted that this operating principle also applies to a diode in which thefirst emitter 11 is n-doped and the second emitter 12 is p-doped. Inthis case, the first electrode 31 forms a cathode and the secondelectrode 32 forms an anode of the diode, and the polarity of thecontrol voltage is to be inverted.

Terms such as “first”, “second”, and the like, are used to describevarious elements, regions, sections, etc. and are not intended to belimiting. Like terms refer to like elements throughout the description.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method of controlling the breakdown voltage ofa diode, the method comprising: providing a diode which comprises asemiconductor body, a first emitter region of a first conductivity type,a second emitter region of a second conductivity type, a base regionarranged between the first and second emitter regions and having a lowerdoping concentration than the first and second emitter regions, a firstemitter electrode electrically coupled to the first emitter region, asecond emitter electrode in electrical contact with the second emitterregion, a control electrode arrangement comprising a first controlelectrode section and a first dielectric layer arranged between thefirst control electrode section and the semiconductor body, and at leastone pn junction extending to the first dielectric layer, or arrangeddistant to the first dielectric layer by less than 250 nm; and adjustinga breakdown voltage of the diode by applying a control potential to thefirst control electrode section.
 2. The method of claim 1, wherein thefirst emitter region comprises a contact region having a higher dopingconcentration than other regions of the emitter region, and the firstemitter electrode is electrically connected to the contact region. 3.The method of claim 1, wherein the pn junction is formed between thebase region and the first emitter region.
 4. The method of claim 1,wherein the diode further comprises a Zener region arranged between thebase region and the second emitter region, and wherein a doping type ofthe Zener region is such that the pn junction is formed between theZener region and the second emitter region or between the Zener regionand the base region.
 5. The method of claim 1, wherein the diode furthercomprises a first control terminal of the first control electrodesection.
 6. The method of claim 1, wherein the control electrodearrangement further comprises: a second control electrode sectionarranged distant to the first control electrode section; and a seconddielectric layer arranged between the second control electrode sectionand the semiconductor body.
 7. The method of claim 1, wherein thesemiconductor body comprises a first surface, and wherein the diodefurther comprises first gate electrode sections arranged in trenchesextending from the first surface into the semiconductor body.
 8. Themethod of claim 7, wherein the first and second emitter regions arearranged distant from one another in a vertical direction of thesemiconductor body.
 9. The method of claim 8, wherein the base regionhas a length in the vertical direction of the semiconductor body, andwherein the first and second control electrode sections extend alongmore than 25%, more than 50%, more than 75%, or more than 100% of thelength of the base region.
 10. The method of claim 8, wherein the baseregion is of the second conductivity type.
 11. The method of claim 1,wherein the semiconductor body comprises a first surface, wherein thefirst and second emitter regions extend from the first surface into thesemiconductor body, and wherein the first and second emitter regions arelaterally separated from one another in a direction that is parallel tothe first surface.
 12. The method of claim 11, wherein the base regionhas a length in a vertical direction, and wherein the first and secondcontrol electrode in the vertical direction of the semiconductor bodyextend at least as far into the semiconductor body as the second emitterregion.
 13. The method of claim 11, wherein the base region is of thefirst conductivity type.
 14. The method of claim 4, wherein the Zenerregion adjoins the second emitter region in a vertical direction of thesemiconductor body.
 15. The method of claim 14, wherein at least one ofthe second emitter region and the Zener region has a lower dopingconcentration in a region in which the second emitter region and theZener region adjoin one another.
 16. The method of claim 1, wherein thefirst emitter region and the second emitter region both extend to onesurface of the semiconductor body, and wherein the first emitter regionfurther comprises: a first emitter section which in a vertical directionof the semiconductor body is arranged distant to the second emitterregion; and a second emitter section arranged distant to the secondemitter in a horizontal direction and in the vertical directionextending from the surface to, the first section.
 17. The method ofclaim 1, wherein the base region has a length in the vertical directionof the semiconductor body that is a shortest distance between the firstemitter region and the second emitter region, and wherein a distancebetween the first control electrode section and the second emitterregion is less than 75% of the length of the base region.
 18. The methodof claim 1, wherein the first control electrode section extends alongthe entire length of the base region.
 19. The method of claim 6, whereinthe first and second control electrode sections form a single controlelectrode that forms a closed loop in a direction parallel to a firstsurface of the semiconductor body.